Torque responsive clutch control

ABSTRACT

The engine output torque of a motor vehicle is a function of the extent to which the throttle valve is open, the further the valve is open, the greater the throttle angle and the greater the output torque. Microprocessor based clutch control is provided to measure the throttle angle, determine the output torque, and automatically engage and disengage the clutch with respect to time. The clutch control also allows manual gear operation and clutch slip control.

This invention concerns controlling operation of clutch means in a motorvehicle.

The motor vehicle is of a type (hereinafter called "the type referredto") comprising

an internal combustion engine to generate engine torque,

fuel supply means to supply fuel to the engine, said fuel supply meanshaving a torque demand condition having a torque demand value which isselectively variable over a range of values extending from a minimum toa maximum demand for torque, the fuel supply means being controllablewhereby the amount of fuel supplied is variable with variation in saidtorque demand value, and wherein the engine power output is increasablein response to increasing the fuel supply to said engine,

drive line means to transmit rotary motion from the engine to at leastone ground running wheel, said drive line means comprising changeableratio gear means and clutch means between said engine and said gearmeans whereby the power output from the engine is input to the clutchmeans to be transmitted by the clutch means to give a power outputproviding a power input to the gear means, and said clutch means havinga torque transmitting capacity which is variable between a predeterminedmaximum and zero whereby when the torque input to the clutch meansexceeds the transmitting capacity clutch slip occurs and the poweroutput is less than the power input to said clutch means, and

control means for automatically causing a reduction of said torquetransmitting capacity upon a demand for a change of ratio in said gearmeans being observed by said control means and for automaticallyincreasing said torque transmitting capacity subsequent to the ratiochange being effected.

In a first known form of motor vehicle of the type referred to the gearmeans, clutch means and control means all form a fully automatic gearbox system in which gear ratio changes are automatically performed inresponse to signal inputs to the control means. The signal inputsrepresent, for example, engine speed and the torque demand value, andare provided from sensors. A gear ratio change takes place when theinput signals have certain predetermined values.

In an automatic gearbox having a torque converter and a lock-up clutch,the torque transmitting capacity of the lock-up clutch may be merelyreduced when a gear ratio change is required and performed, andsubsequent to the ratio change the torque transmitting capacity of thelock-up clutch is increased again.

In a second known form of vehicle of the type referred to the clutchmeans and control means form a semi-automatic transmission system inwhich the vehicle has no clutch pedal but has a gearbox in which thegear ratio changes are performed or at least initiated by manual actionby the driver. Gear ratio changes may be effected by the manual effortexerted by the driver moving a gear lever when the driver desires thegear ratio change to be made or the changes may be powered by motormeans, for example electric or fluid powered motors or actuators inresponse the driver operating manual means, for example a lever, switchor push-button. The initiating and completing of such a gear ratiochange are detected by sensor means and corresponding signals sent tothe control means which automatically causes the torque transmittingcapacity of the clutch means to be reduced to zero just before the ratiochange and automatically restores torque transmitting capacityimmediately after the ratio change. Whether or not a gear change is madeis at the driver's discretion and irrespective of a fuel supplymagnitude demand signal being sent, for example via a mechanical linkagefrom an accelerator pedal, to a control of the torque demand conditionof the fuel supply means. To prevent the engine racing during a changeof gear ratio the control means may also provide an override fuel supplymagnitude demand signal (capable of overriding the signal from theaccelerator pedal) to automatically ensure that the supply of fuel is ofa low amount whilst the torque transmitting capacity of the clutch meansis zero.

In the case of both the first and second forms of vehicle a jolt andvibrations can occur at tip-in. Tip-in is a situation where initiallythe vehicle is travelling forwards with the accelerator pedal in aposition corresponding to a demand for a low supply of fuel to theengine (i.e. a low engine torque demand), and the vehicle is in acondition of over-run where the momentum of the vehicle is driving theengine; then the accelerator pedal is suddenly depressed or tipped-in bythe driver. This causes a sudden increase in the supply of fuel to theengine and a rapid increase in engine output torque. Accordingly thereis a sudden surge in the torque in the drive line means which causesfree play in the drive line means to be taken up as the drivingdirection suddenly reverses from over-run to engine drive. It is thistaking-up of free play which causes the jolt and vibrations, and thesedisturbances are felt by the driver who may find the experience anuisance or disconcerting in addition to any damaging effect thedisturbances may have on the drive line means.

An object of the invention is to provide a vehicle of the type referredto in which large torque surges in the drive line means at tip-in, or atsome other sudden increase in demand for fuel from a low level ofdemand, are avoided or at least reduced.

According to the invention there is provided a motor vehicle of the typereferred further comprising observing means to produce a torque demandvalue signal which is a function of said torque demand value saidcontrol means being responsive to said torque demand valuesignal andarranged to control the clutch means in a manner which produces a torquetransmitting capacity in the clutch means which is a function of saidtorque demand value whereby at least below a predetermined magnitude ofsaid torque demand value the torque transmitting capacity of said clutchmeans is less than said maximum, and the control mean being arrangedsuch that whilst the vehicle continues to run in the same gear ratio andthere is an occurrence of a said torque demand value signal signifyingan increase in said torque demand value from a magnitude less than saidpredetermined magnitude the control means automatically responds toincrease the torque transmitting capacity of the clutch means such thatduring at least part of the time of said increase the torquetransmitting capacity of the clutch means is less that the output torquefrom the engine whereby slipping of said clutch means occurs.

In the fuel supply means, the torque demand condition at any instant maybe (or may be a function of) the attitude or position of a relativelymovable component part of the fuel supply means, the position of whichcomponent part is a function of the amount of fuel being supplied. Forexample, in the case of a petrol driven engine, the fuel supply meansmay comprise a carburetor or a fuel injection system. In either case thetorque demand condition can be the attitude of a throttle valvecontrolling the size of a throttle opening or can be the size of thethrottle opening. For example, the torque demand value corresponding tothe minimum demand for torque can correspond to the throttle openingbeing of a minimum size set by the throttle valve, i.e., 0% throttle andthe torque demand value corresponding to a maximum demand for torque cancorrespond to the throttle opening being of maximum size set by thethrottle valve, i.e., 100% throttle. When the engine is a diesel enginethe fuel supply means may comprise a fuel pump in which the torquedemand value of the torque demand condition may be represented by or bea function of the condition or position of the rack. In the case of bothpetrol and diesel engines, the torque demand value can be represented byor be a function of the accelerator pedal position at any instant withrespect to a reference position for the pedal.

The invention will now be further described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a diagrammatic illustration of a motor vehicle formedaccording to the invention:

FIG. 2 is a diagrammatic illustration partly in section of an internalcombustion engine with a carburetor, and drive line means comprising anautomatic gear box for the vehicle in FIG.1;

FIG.3 is a fragment diagrammatically illustrating a modification to thearrangement in FIG.2 wherein the carburetor is replaced by fuelinjection means;

FIG. 4 is a set of diagrams or graphical representations illustratingoperation of the clutch means in relation to the throttle opening sizein the vehicle formed according to the invention in FIG.1;

FIG.5 is a set of diagrams or graphical representations, of variation ofthrottle angle ta and drive line torque dlt with respect to time t, andillustrate in full lines a sudden increase in drive line torque dlt inresponse to a sudden increase in demand for fuel at tip-in in a knownmotor vehicle; the torque shown in dash line illustrating an objectiveit is desired to aspire towards in a motor vehicle formed according tothe invention, and

FIG. 6 shows a modification which can be applied to the vehicle in FIG.1and is a diagrammatic illustration partly in section of an internalcombustion engine with fuel supply means and drive line means comprisinga semi-automatic transmission.

In the drawings like or similar parts are identified by the samereference numerals.

With reference to FIG.5, in a known motor vehicle of the type referredto in which fuel and air is supplied to the internal combustion engineby means of a carburetor, the carburetor has a throttle comprising aninduction passage which can be opened and closed by varying amounts by abutterfly throttle valve. The extent to which the passage is opened orclosed being the throttle size determined by the position or angle(throttle angle ta), between maximum and minimum values, of the throttlevalve i.e. the greater the throttle angle the greater the throttle size,and therefore the greater the value of the torque demand condition inthe fuel supply means comprising the carburetor. The amount of fuel andair supplied to the engine via the throttle is in a direct proportion tothe throttle angle. At tip-in the throttle angle ta is suddenlyincreased as indicated at A in FIG. 5, the consequence on drive linetorque dlt is a torque surge spike B and torque fluctuation C causingthe aforementioned jolt and vibrations.

With a view to ironing out the torque spike B and fluctuations C, themotor vehicle to be described with reference to FIGS. 1 to 4 endeavoursat tip-in, to increase drive line torque dlt in accordance with dashpart D (FIG.5).

VEHICLE WITH AUTOMATIC TRANSMISSION

Referring now to FIGS. 1 and 2, a motor vehicle 2 has front groundrunning wheels 4, rear wheels 6, an internal combustion engine 8 anddrive line means comprising an automatic gear box 10 driving the twofront wheels 4 (only one shown). In addition or alternatively, the rearwheels could be driven.

The automatic gear box 10 comprises a clutch system 12, a gear box 14,an hydraulic control 16, and an electronic control 18 comprisingcomputer means containing a predetermined controlling program.

The clutch system 12 is a twin clutch system represented purelyillustratively and may be of the wet plate kind. It has a pair of drivenclutch plates 20 and 22 each splined to a respective gear box inputshaft 24 and 26. The clutch system has a rotatable cover 28 secured torotate with an engine fly-wheel 30. Both rotationally and axially fastwith the cover 28 is an annular clutch counter-pressure plate 32. A pairof annular clutch pressure plates 34 and 36 are splined at theirperipheries to the cover 28 so as to be rotationally fast therewith butaxially slidable relatively to the cover. Diaphragm springs 38 and 40are arranged for acting respectively on the pressure plates 34 and 36.Associated with each spring 38, 40 is a respective thrust member 42 or44 formed as an annular piston sliding in a respective hydrauliccylinder 46 or 48 at each end of the clutch cover 28. The clutch cover28 can rotate relatively to the shafts 24 and 26 and relatively tostationary, annular, hydraulic supply cuffs 50 and 52 enabling thesupply of hydraulic pressure to the cylinders 46 and 48 respectively viaconduits 54 and 56 and the relief of hydraulic pressure in the cylindersalso via the conduits. Accordingly, applying hydraulic pressure to thecylinder 46 urges the thrust member 42 which pushes the diaphragm spring38 which urges the pressure plate 34 to clamp the clutch driven plate 20against the counter-pressure plate 32. Since the torque transmittingcapability or capacity of engaged clutch 34, 20, 32 (hereinafter calledClutch I) is directly proportional to the force with which the drivenplate 20 is clamped against the counter-pressure plate 32 it followsthat the torque transmitting capacity of the engaged Clutch I isdirectly proportional to the hydraulic pressure in the cylinder 46, i.e.the greater the hydraulic pressure the greater the torque transmittingcapacity. Relieving the hydraulic pressure in the chamber 46 allows theClutch I to disengage and eventually reduces its torque transmittingcapacity to zero. The other clutch 36, 20, 32 (hereinafter called ClutchII) is operated by applying and relieving hydraulic pressure via conduit56, the operation of Clutch II being substantially similar to that ofClutch I. When the Clutch II is engaged it has some torque transmittingcapacity, and torque up to the value of that capacity can be input tothe gear box 14 by the sleeve shaft 26. Whereas if Clutch I is engagedtorque up to its capacity value can be input to the gear box 14 by theshaft 24.

The change speed gear box 14 is represented diagrammatically andsymbolically and can provide six selectable gear ratio changes eachgiving a corresponding torque output on output shaft 58 for transmissionto the road wheels 4. The six changeable ratios constitute first,second, third, fourth, fifth and reverse gears. The gear box 14 includeshydraulically operated gear engagement means (not shown) operated inaccordance with the hydraulic pressures obtaining in conduits 61, 62,63, 64, 65 and 66 as controlled by the hydraulic control 16 alsoconnected to the conduits 54 and 56.

The arrangement is such that when any one of the first, third or fifthgear is engaged the vehicle is only driven by that gear when Clutch I isengaged, and when any one of the second, fourth or reverse gear isengaged the vehicle is only driven by that engaged gear when Clutch IIis engaged. Also the controls 16 and 18 are arranged so that when ClutchI engages, Clutch II automatically disengages and vice-versa.

Hydraulic pressure sensors 72 and 74 ar provided in the conduits 54 and56 to provide electrical signals indicative of the fluid pressuresobtaining in those conduits, the electrical signals being transmitted toan interface 76. Associated with the gear box 14 are gear engagedindicators 78, 80 and 82 transmitting to the interface 76 electricalsignals indicating which of the first, second, third, fourth, fifth orreverse gears has/have been engaged. The interface 76 further receivesfrom transducer 84 an electrical signal indicative of the engine speedand on channel 85, from transducer 86 an electrical signal indicative ofthrottle opening size in fuel supply means 88 formed by a carburetorwith an air filter 90. The carburetor comprises a float chamber 92, afuel jet 94 and a throttle comprising an induction passage 96 containinga pivotable throttle valve 98. The vehicle has an accelerator pedal 100which can be connected mechanically by known means to the throttle valve98 so that the more the pedal is depressed the more the throttle valveis rotated away from its position corresponding to minimum throttleopening towards its position of maximum throttle opening, the valve 98returning towards its minimum throttle position as the pedal isreleased. For any given engine speed the more the throttle is opened thegreater the amount of fuel and air supplied to the engine 8. Thethrottle at minimum size may be referred to as 0% throttle or thethrottle valve 98 as being at 0° throttle angle. At maximum size thethrottle may be referred to as 100% throttle, the throttle valve 98having been rotated through its greatest extent, for example about 80°or so, from its minimum throttle position to open wide the passage 96;i.e. passage 96 is wide open at a throttle angle of 80° or so. Thereforethe transducer 86 may be arranged to observe the angular position of thethrottle valve 98, relative to its position at minimum throttle size andprovide an electrical signal indicative of the relative angular positionof the throttle valve (throttle angle) and thus indicative of the sizeof the throttle opening which is thus indicative of the amount of fueland air being supplied to the engine 8. Alternatively since there is acorrespondence between the size of the throttle opening and the positionof the accelerator pedal 100, the transducer 86 could be arranged toobserve the position of the pedal and provide the signal indicative ofthrottle opening size corresponding to the. pedal position. Instead of amechanical (or hydraulic) link between the pedal 100 and the throttlevalve 98 the link could be of a kind wherein the throttle valve 98 isrotated by motor means, for example an electric motor, in response toelectric or other signals produced by a signal generator in accordancewith the position of the accelerator pedal 100.

The alternative fuel supply means 88 A in FIG.3 is a fuel injectionsystem in which fuel injector means 102 in response to signals on 104from an electronic control, for example the control 18, supplies fuel tothe engine 8 in amounts directly proportional to the size of thethrottle opening as determined by the angular position of the throttlevalve 98 observed by the transducer 86.

Interface 76 may be arranged to digitise or otherwise render theelectrical signal inputs thereto compatable with the computer 18 toserve as data inputs to the latter. Output signals from computer 18 areinput to an interface 106 which converts them to signals, for exampleanalogue signals, compatable with the hydraulic control 16.

The computer control 18 is loaded with a program comprising gear ratiorunning and gear ratio changing maps which, in accordance with theengine speed and throttle angle data supplied to control 18, determinesthrough which gear ratio drive is required of any instant. Control 18also anticipates in the case of drive through second, third and fourthgears which is the next likely gear ratio (up or down) through whichdrive will be required and causes that ratio to be engaged whilst theClutch I or II corresponding to that ratio is in a disengaged state. Inthe case of driving through the first gear ratio, the second gear ratiois caused to be automatically in engagement by the control 18 inreadiness (Clutch II being in disengaged state). Whereas when driving isthrough the fifth gear ratio the control 18 automatically causes thefourth gear ratio to be in engagement in readiness (Clutch II beingagain in disengaged state). If, for example, driving is through thesecond gear ratio the computer control 18 has caused hydraulic control16 to apply hydraulic pressure on conduit 62 to engage the second gearratio and has caused the relief of hydraulic pressure in conduit 54 sothat Clutch I is disengaged and the application of pressure on conduit56 to engage Clutch II. In relation to the program maps the computercontrol analyses the engine speed and throttle angle data itcontinuously receives and determines what is the next likely gear changeto be needed. If it is to be a change up then the computer control 18instructs the hydraulic control 16 to supply pressure on conduit 63 toengage the third gear ratio. If the data inputs to computer 18eventually satisfy the program criteria corresponding to running inthird gear, the computer instructs hydraulic control 16 to relieve thepressure in conduit 56 so that Clutch II disengages whilstsimultaneously applying pressure on conduit 54 to engage Clutch I.Therefore driving ceases to be through second gear and becomesestablished through third gear.

Manual means (not shown) can be provided to operate the hydrauliccontrol 16 to cause the engagement of the reverse gear ratio by pressureon conduit 66 and the engagement of Clutch II when drive through reversegear is required.

In the automatic gear box 10, the torque transmitting capacity of ClutchI or Clutch II is directly proportional to the hydraulic pressure incylinder 46 or 48 respectively. That hydraulic pressure is a function ofboth the engine speed and the throttle angle and is provided by thehydraulic control 16 under instructions from computer control 18programmed to instruct the desired hydraulic pressure in accordance withthe engine speed and throttle angle data the computer receives, whengear changing is taking place or the vehicle is running in any gearratio.

When the vehicle is running in any gear ratio the torque transmittingcapacity of the corresponding Clutch I or II has a predetermined maximumvalue (capable of transmitting the maximum engine output torque to thegear box 14) in consequence of applying a predetermined maximumhydraulic pressure to the cylinder 46 and 48.

TIP-IN CONTROL

In FIG. 4 variation in throttle angle ta and clutch torque transmittingcapacity tc are shown with respect to time t.

With reference to FIG.4, if one takes as an example that the vehicle isrunning in fourth gear, section e of the torque diagram shows thatClutch II has the aforesaid predetermined maximum torque transmittingcapacity due to the pressure in cylinder 48 being at the predeterminedmaximum. Furthermore it will be assumed that the engine speed remainswithin a predetermined speed range such that the computer 18 will notinstruct a gear change.

If the driver releases the accelerator pedal the throttle angle tadecreases as signified by section F in FIG.4. A throttle angle value xis predetermined or selected being an appropriate maximum throttle anglebelow which the occurrence of transmission line disturbance, inconsequence of a sudden increase in throttle angle, is to be eliminatedor at least reduced. The throttle angle x can be called the "tip-inthreshold" and may be a few degrees, for example substantially 10° .When the throttle angle ta decreases to at least the "tip-in threshold"a section of program, in computer 18, provided for tip-in control comesinto effect. As a result, below the tip-in threshold the torquetransmitting capacity of the clutch is modulated by the throttle angle,and the computer calculates a detect reference DR which (for the timebeing) may be simply understood as a numerical value equal to thethrottle angle plus a small positive, numerical "detect off-set". Thatdetect off-set is a predetermined number of angular degrees, for examplesubstantially 2°. For a throttle angle of 7° the calculated detectreference would be 9° (i.e. 7°+2°). Therefore as the throttle angledecreases in accordance with section F in FIG. 4, when it falls belowthe tip-in threshold x the computer 18 instructs the hydraulic control16 to relieve pressure in clutch cylinder 48 (FIG.2) to reduce thetorque capacity tc of Clutch II as indicated by diagram section f untilit reaches a constant value at section g for the constant throttle angleat section G for which the computer has also established the detectreference value shown by section DR1. The value of the torque capacitybelow tip-in threshold at any constant throttle angle is calculated bythe computer 18 and controlled thereby in accordance with the throttleangle and engine speed data so that the torque capacity of the Clutch IIis slightly greater than the torque input thereto from the gear box todrive the engine; i.e. the torque capacity of the clutch is just enoughto transmit the torque which is input into the clutch.

If the throttle angle is reduced again as shown at section H in FIG.4 toa constant value represented at . section J, the clutch torque capacityis quickly dropped further through section h to the value at section jand a new lower detect reference DR2 is established in the computer 18.

Should, for example, the throttle angle now be suddenly increasedslightly, as indicated at section K, by an amount less than the detectoff-set, the level of the detect reference is maintained at DR2 eventhough the throttle angle at the steady section V is greater than a J.However, the computer control responds to the increase in throttle angleand over a time constant T1 causes the hydraulic control 16 to increasethe hydraulic pressure in cylinder 48 (FIG.2) substantiallyexponentially to increase the clutch torque capacity at a controlledsubstantially exponential rate as represented at section v1 for example,up to a steady value represented at section v2.

Whilst the clutch torque capacity is being increased in accordance withsection v1 it is possible that some clutch slip may occur before thecapacity represented by v2 is substantially attained. The time durationT1 can be small for example substantially in the range of 300.0milliseconds to 500.0 milliseconds, preferably substantially 300millseconds.

Should the throttle angle be reduced to a smaller value represented bysection M, then, because this is a reduction in throttle angle, thecomputer 18 calculates a new detect reference value shown at DR3, whichis smaller than DR2. Also the torque transmitting capacity of the clutchis ramped down quickly to the throttle angle modulated level at sectionm.

Increasing the throttle angle suddenly to a steady value represented bysection N gives the throttle angle a value greater than the currentdetect reference DR3 but less than the tip-in threshold. Immediately thethrottle angle is increased, the computer control begins to cause somevery small increase (section n1) in clutch torque transmitting capacity.But at the same time the computer control initiates timer means tomeasure a time duration T2. Because the computer control observes thatthe throttle angle has increased above the detect reference, theaforementioned increase in clutch torque capacity is rapidly stopped andthe time delay T2 brought into effect. Therefore the clutch torquecapacity is held at a low steady level (section n2) until the relativelyshort time delay T2, for example substantially 100.0 milliseconds,expires. Then the computer control 18 causes the torque transmittingcapacity of the clutch to increase over the time T1, substantiallyexponentially (as indicated by section n3) up to a steady valueindicated at section n4. The controlled rate of increase at n3 delaysthe time that the required torque capacity of n4 is attained.Consequently during the increase at n3 the torque transmitting capacityof the clutch is less than the capacity needed to transmit all the powerwhich is input to the clutch. Thus at section n3 clutch slip occurs toreduce the chance of transmitting torque surge to the gear box from theengine.

When a driver suddenly presses on the accelerator to rapidly increasethe throttle angle, there is a short delay before the increased chargeof fuel and air reaches the engine. Thus there is a short delay beforethe engine produces the torque surge due to that increased charge. Byintroducing the time delay T2 to hold down the torque transmittingcapacity of the clutch for that time delay, there is a greater chancethat the torque surge from the engine will coincide with the controlledrate of increase in torque capacity at n3 so that the clutch slip ismore likely to occur at the time of the surge. Therefore tranmission ofthe surge by the clutch should not occur.

When the timer means in the computer 18 measuring the time delay T2times out, two further timer means commence in the computer. Onemeasures the time T1 and the other measures time duration T3 which isthe reset detect reference time. At the end of reset time T3, the detectreference is increased by the computer control to its new value DR4. T3is not shorter than T1 and is preferably longer, for examplesubstantially 500.0 milliseconds.

Regarding the detect reference DR4 and the detect references DR1, DR2and DR3, it will be understood that whilst the throttle angle remainsnot greater than each of the tip-in threshold and the detect reference,then each time the throttle angle drops below its previous minimum valuethe detect reference is set at a new lower level. Whereas whilst thethrottle angle remains below the tip-in threshold, a new increaseddetect reference is only set by the throttle angle being increased abovethe current detect reference.

Also when an increase in throttle angle is less (such as represented bysection K) than the detect off-set, no time delay T2 is introducedbefore the torque transmitting capacity of the clutch is increased atthe controlled rate over the time T1.

Taking a case where the throttle angle, for example as represented atsection N (FIG.4), is below both the tip-in threshold x and the detectreference, for example DR4, now if the throttle angle is suddenlyincreased to a value (such as represented by section P) above both thedetect reference and the tip-in threshold, this can be considered astip-in proper. Because the throttle angle increases above the tip-inthreshold DR4 the time delay T2 comes into operation and the clutchtorque transmitting capacity is held down as represented by section p2.When the delay T2 expires the clutch torque transmitting capacity isincreased by the computer control 18 substantially exponentially, asrepresented by section p3, over the time T1 up to the value representedby section p4 which again is just greater than that needed by the clutchto transmit all the power which is input thereto. Thus again whilst thetorque transmitting capacity is being increased in accordance withsection p3 clutch slip occurs to reduce the chance of transmittingtorque surges from engine to gear box. At the same time as one of thetimer means starts to measure the time T1, other timer means in thecomputer starts to measure a time T4 (which is relatively long, forexample substantially 1.0 second) because the throttle angle is now inexcess of the tip-in threshold. When time T4 expires computer control 18exits from the section of program concerned with tip-in control and,under instruction from another program section, ramps up the torquetransmitting capacity of the clutch to the predetermined maximumrepresented at section p5. Furthermore, because the throttle angle ta isnow above the tip-in threshold no new detect reference is calculated andreference DR4 goes void at the expiry of timeout T4.

In a modification of the control which can come into effect when thethrottle angle is increased above the detect reference (if the increasein throttle angle is measured by the computer 18 as being in excess of apre-determined rate) then whilst the delay time T2 is being measured outthe torque transmitting capacity of the clutch is dropped (asrepresented by dotted sections r1 or s1) to a value less than thecapacity which was needed to transmit all the power input to the clutchimmediately before the increase in throttle angle. On the delay T2expiring, the clutch torque transmitting capacity is increased at acontrolled exponential rate shown at dotted section r3 or s3 up to theaforementioned values at n4 or p4. By so dropping the torque capacityand then increasing it in the controlled manner, the chance of thetransmission of torque surges from the engine is much reduced. It isbelieved that this modification should only be used for relatively highrates of increase of the throttle angle. If it were used at low rates ofincrease, it might be detrimental to the engine braking effect duringover-run.

With reference to FIG.4 the tip-in control has been described withreference to operation of the Clutch II whilst the vehicle is running infourth gear, tip-in control can be applied in comparable manner to theoperation of Clutch II whilst the vehicle is in second gear and to theoperation of the Clutch I when the vehicle is running in first, third orfifth gear.

VEHICLE WITH SEMI-AUTOMATIC TRANSMISSION

The semi-automatic transmission concerned is of a kind (hereinaftercalled the kind referred to) comprising change-speed gear means having aplurality of mutually exclusive selectable gear ratio means, gear ratioselection means operable when desired by the driver to select a desiredsaid gear ratio, clutch means interposed between the engine and a rotarymotion input shaft to said change-speed gear means, and clutch controlmeans to automatically disengage said clutch means upon occurrence of agear ratio change demand signal initiated by the driver and toautomatically re-engage said clutch means upon subsequent occurrence ofa gear ratio selection.

With reference to FIG. 6 an internal combustion engine is shown at 202,and at 204 a semi-automatic transmission of the kind referred to for amotor vehicle. The transmission comprises a clutch 205, for example adiaphragm spring clutch, within a bell-housing 206 and a change-speedgearbox 208 having an output shaft 210 for supplying rotary drive to oneor more road wheels, and a rotary motion input shaft (not shown) onwhich is mounted in known manner a clutch driven plate. Gearbox 208comprises a plurality of mutually exclusively selectable gear ratios(know per se) any desired one of which is selectable (in the course of adriver making a gear change) by a suitable pre-determined manualmovement of a gear shift lever 212 to dis-engage or de-select the saidratio currently selected and then select or engage any desired said gearratio. A clutch control for automatically engaging and disengaging theclutch comprises an electronic control 214 and a fluid flow control 216.The electronic control comprises computer means. The clutch isdisengaged and re-engaged using a release lever or fork 218 pivoted at220 and interacting in known manner with the clutch. A fluid pressurepiston and cylinder unit or actuator 222 acts on the lever 218 so thatthe rate and degree of engagement or disengagement of the clutch at anyinstant is controlled by the amount of fluid in the actuator 222. Theamount of fluid, which may be hydraulic fluid, acting in actuator 222 iscontrolled by a fluid pressure supply and control system 224 forming thefluid flow control 216 with the actuator. Shift lever 212 includes ashaft 226 provided with a known gear lever pivot 228 permitting theshift lever a degree of universal movement. Shaft 226 is connected byany means 230 known per se for conveying movement of the shift lever 212to a selection crank arm 232 causing selection and de-selection of anydesired said gear ratio when the shift lever 212 is moved according tothe gear shift pattern. In addition to the shaft 226 the gear shiftlever 212 also comprises a tube 234 (shown in section) surmounted by aknob 236. Tube 234 is mounted by a pivot 238 on the shaft 226. Knob 236is intended for application of manual force directly thereto by the handof the driver, for changing gear. When no manual force is applied thetube 234 adopts a centralised or initial position with respect to theshaft 226 under the action of resilient means (not shown) acting betweenthe shaft and tube. On the other hand when sufficient manual force isapplied to the knob 236 the tube 234 initially tilts slightly relativeto the lever 226, about pivot 238, before the lever 226 is moved byfurther force on the tube to move the selection crank arm 232. Thisinitial tilting of the tube 234 is taken as indicating a wish by thedriver to change gear, and tilt sensor means 240 gives a tilt signal onchannel 242 when a tilt has occurred. In response the electronic control214 gives an output disengage clutch signal on channel 244 causingclutch control 216 to automatically disengage the clutch 205,thereafter, selection of any desired gear ratio is observed by sensor246 providing a gear selection completed signal on channel 248. Inresponse the control 214 gives an output re-engage clutch signal onchannel 244 causing the control 216 to automatically re-engage theclutch 205.

The extent of clutch engagement or torque transmitting capacity of theclutch 205 is a function of the fluid pressure prevailing in theactuator 222 which is provided with a pressure sensor 250 to provide anoutput signal on channel 252 corresponding to the torque transmittingcapacity of the clutch. Alternatively this same information could beprovided by a sensor observing the position of a piston in the actuator222 or observing the attitude of the release fork 218. Throttletransducer 86 provides signals on channel 254 representative of thethrottle opening size.

The computer in the electronic control 214 is programmed to vary thetorque transmitting capacity of the clutch 205 in the same manner as thetorque transmitting capacity tc is varied as described above withreference to FIG.4 when the throttle angle in the system in FIG. 6 isvaried in like manner to the variation of the throttle angle ta inFIG.4.

If desired the selection crank arm 232 can be moved to change gear bymotor means or by fluid pressure operated actuator means. In either casethe motor means or the actuator means respond to control meansresponsive to manual operation, by the driver, of lever, switch, orpush-button means.

It will be appreciated that if the engine 8 or 202 is a diesel enginethen the fuel supply means 88 in the form a carburetor in FIG.2 and 6would be replaced by an in injection and fuel pump system controlled byan accelerator pedal. In most cases the transducer 86 could be arrangedto observe the attitude or position of either a fuel rack or a controltherefore or to observe the position of the accelerator pedal.

VEHICLE WITH ALTERNATIVE AUTOMATIC GEARBOX

In a motor vehicle having an automatic gearbox with a torque convertorand an hydraulically operated lock-up clutch, that clutch can be slippedat tip-in and operated in a manner similar to that shown in anddescribed above with reference to FIG.4.

We claim:
 1. A motor vehicle comprising:an internal combustion engine togenerate engine torque, fuel supply means to supply fuel to the engine,said fuel supply means having a torque demand condition having a torquedemand value which is selectively variable over a range of valuesextending from a minimum to a maximum demand for torque, the fuel supplymeans being controllable whereby the amount of fuel supplied is variablewith variation in said torque demand value, and wherein the engine poweroutput is increasable in response to increasing the fuel supply to saidengine, drive line means to transmit rotary motion from the engine to atleast one ground running wheel, said drive line means comprisingchangeable ratio gear means and clutch means between said engine andsaid gear means whereby the engine power output is input to the clutchmeans to be transmitted by the clutch means to give a power outputproviding a power input to the gear means, and said clutch means havinga torque transmitting capacity which is variable between a predeterminedmaximum and zero whereby when the torque input to the clutch meansexceeds the transmitting capacity clutch slip occurs and the poweroutput is less than the power input to said clutch means, and controlmeans for automatically causing a reduction of said torque transmittingcapacity upon a demand for a change of ratio in said gear means beingobserved by said control means and for automatically increasing saidtorque transmitting capacity subsequent to the ratio change beingeffected, and observing means to observe and produce a tip-in signalwhich is a function of said torque demand value, said control meansbeing responsive to said torque demand value signal and arranged tocontrol the clutch means in a manner which produces a torquetransmitting capacity in the clutch means which is a function of saidtorque demand value whereby at least below a predetermined magnitude ofsaid torque demand value the torque transmitting capacity of said clutchmeans is less than said maximum, and the control means being arrangedsuch that whilst the vehicle continues to run in the same gear ratio andthere is an occurrence of a said tip-in signal signifying an increase insaid torque demand value from a magnitude less than said predeterminedmagnitude the control means automatically responds to increase thetorque transmitting capacity of the clutch means such that during atleast part of the time of said increase the torque transmitting capacityof the clutch means is less than the output torque from the enginewhereby slipping of said clutch means occurs.
 2. A motor vehicle asclaimed in claim 1, wherein in response to occurrence of a said tip-insignal said control means automatically causes an increase in the torquetransmitting capacity of the clutch means over a predetermined period oftime.
 3. A motor vehicle as claimed in claim 1 wherein when the torquedemand value is less than said predetermined magnitude said controlmeans is arranged to set the torque transmitting capacity to the clutchmeans at a value which is slightly more than that needed for the clutchmeans to transmit the power which is being input to the clutch means andon occurrence of a said tip-in signal said control means is arranged torespond to increase the clutch torque transmitting capacity from a valueset before said occurrence to an increased set value.
 4. A motor vehicleas claimed in claim 1 wherein the rate of increase in torquetransmitting capacity of the clutch means is substantially anexponential increase in capacity with respect to time.
 5. A motorvehicle as claimed in claim 1 wherein said control means (16, 18; 214,216) is arranged such that at the occurrence of a said tip-in signal theincrease in clutch torque transmitting capacity is substantiallyinitiated after a time delay from the occurrence of said tip-in signal.6. A motor vehicle as claimed in claim 1 wherein the control means isarranged to respond to an occurrence of a said tip-in signal to reducethe torque transmitting capacity of the clutch means before said torquetransmitting capacity is automatically increased as a consequence of theoccurrence of said tip-in signal.
 7. A motor vehicle as claimed in claim6, wherein the rate of said increase in the torque transmitting capacityof the clutch means is substantially an exponential increase in capacitywith respect to time subsequent to said decrease in torque transmittingcapacity of the clutch means caused by said control means responding tothe occurrence of a said tip-in signal.
 8. A motor vehicle as claimed inclaim 6 wherein said reduction in torque transmitting capacity occursduring a predetermined time delay.
 9. A motor vehicle as claimed inclaim 5 wherein said time delay is of a predetermined duration.
 10. Amotor vehicle as claimed in claim 1 wherein when the torque demand valueis less than said predetermined magnitude the control means is arrangedto establish a detect reference DR having a value which is apredetermined function of the torque demand value and greater than saidtorque demand value.
 11. A motor vehicle as claimed in claim 10 whereinsaid control means is arranged such that at the occurrence of a saidtip-in signal the increase in clutch torque transmitting capacity issubstantially initiated after a time delay from the occurrence of saidtip-in signal and the control means is arranged so that said time delayoccurs in consequence of said tip-in signal being produced by the torquedemand value increasing to a value at least equal tot he detectreference.
 12. A motor vehicle as claimed in claim 10 wherein thecontrol means is arranged so that when the detect reference valuecurrent at the time of an occurrence of a said tip-in signal is exceededby the increased torque demand value then after a time delay from saidoccurrence of said tip-in signal the control means establishes a newdetect reference having an increased value which is a said function ofthe increased torque demand value.
 13. A motor vehicle as claimed inclaim 10 wherein provided the torque demand value remains below thedetect reference value, the detect reference value is a said function ofthe smallest torque demand value to which the torque demand value hasbeen reduced.
 14. A motor vehicle as claimed in claim 1 wherein thevehicle is provided with an automatic system for automatically changingfrom one gear ratio to another in said changeable ratio gear means,during travel of the vehicle.
 15. A motor vehicle as claimed in claim 1wherein the drive line means comprises a semi-automatic transmission forchanging from one gear auto to another during travel of the vehicle,said semi-automatic transmission comprising change-speed gear meanshaving a plurality of mutually exclusive selectable gear ratio means,gear ratio selective means operable when desired by the driver to selecta desired said gear ratio, clutch means interposed between the engineand a rotary motion input shift to said change-speed gear means, andclutch control means to automatically disengage said clutch means uponoccurrence of a gear ratio change demand signal initiated by the driverand to automatically re-engage said clutch means upon subsequentoccurrence a gear ratio selection.